Try disabling every cache option (except disk cache), and rerun the IOMeter. The random writes should arrive at the right spot then at least, not sure of the reads. (and you don't really need the read-ahead on these).
~12K random writes @4K block = ~50MB/s, presuming 10 sec run time = ~500MB - just about right for the cache to influence it.

It can't add latency, otherwise the queue = 32 random reads would not surpass the 12K mark.
Quote Originally Posted by One_Hertz View Post
That is very interesting. Could you please run IOmeter for me? Just 4KB random reads will do. I have a very strong suspicion that the raid card is adding a lot of latency to the drives and is making reads slower than they should be.